Maybe your partner just had a bad day? I know the people in our dojo, most of them are very nice persons. But still this situations occur from time to time. If I'm training with someone I've been knowing for years it's o.k. Sometimes I can't avoid, too, that I carry some leftovers of a hard day on the mat and I'm glad that there are people who understand. Nobody of us would hurt a partner on purpose. But sometimes it just happens.
Training with new people or someone on a seminar is different. When someone new, especially those who trained in other MA, has to show off by hurting people, they are to be stopped.
And I know someone attending lots of seminars who injurs people really badly where ever he appears. This are people I avoid. All the others get another chance.